Black could have simply finished development with an equal position, but Carlsen decides to capture the pawn, a bold decision that is approved by the computer. I suppose many humans wouldn't dare open the g-file, but Carlsen's instincts, sense of danger, and precision when evaluating a position aren't matched by anyone.
12. e4e5  12... f6d5  13. c3d5  13... b7d5 Now Black is fine since White has to lose a tempo in order to defend the c2-pawn. 14. e2d3 